Modulator



May 25, 1948A K N. H. YOUNG, JR 2,441,983

MODULA'TOR Filed Dec. 6, 1943 2 sheets-sbg@ 1 t s Y' bf 0 A i E (o) y MMM-lll IN VEN TOR. Na/WN H. y0u/v6, JK.

.ATTRWY May 25, 1948. N. H. YOUNG, JR 2,441,983

MoDULAToR Filed Dec. 6, 1945 2 Sheets-Sheet 2 v JNVENTOR. NOP/MN H Y0U/v6, Jf.

ATTORNEY Patented May 25, 1948 2nite assigner to Federal Telephone 4and Radio 'Corporation, New "York, N. @corporation of 'Delaware Ais ciaiigis. (o1. infinis) lhis invention relates .to modulation vsystems andmore .particularly to. a modulator for generating v.pulses time modulated according ,to -a signal vwave.

,in A'the fcopending application of E. VLabin .and D. D. Grieg, Serial No. 455,897, filed August 24, 1942, a push-pull T. M. (time modulation) A.system `-is Idisclosed incorporating .the principle of full-wave .rectification .of ia vsine or triangular wavewhe'reby spaced cuspsare produced and time modulatedpin push-pull manner according to signal energy. The cusps Aare .clipped and, gif desired, .maybe .shaped lto .produce narrow width pulses for transmission.

It isfone ofthe objects. of my invention .to vprovide =a .further .time modulation' system particularlyndaptedfor use .with/triangular base waves or rother v.shaped waves f'having long substantially linearlysinclined,portions whereinit is important to .preserve Vsuch -wave shape prior to rectification.

.'Another :object .of myinventionis to .provide a time modulation system capable of. greater: swings of modulation .with substantially linear :translation df ...the i signal energy :into time :displacement of. thefoutput pulses than possiblebyftime modulators heretofore proposed.

flIheabove .and other objects ancillary thereto willlbecomeimore apparent. upon.- consideration of the :detailed description to. 'be read in .connection with'the accompanying drawings,- in which:

Fig. 1 is a schematic wiring diagram of a time modulation vsystem according to my invention;

Figi-Zie agraphical illustrationuseful in .explaining.the,..operation of the system oflFig. t1; and

Eig isay schematic wiring diagram .illustrating afuither .'embodimentof the invention. l

:ReferringrtoFigs :1 and 2 of the drawing, a circuit wave I2,.curveza,1if.stableifrequency. .The circuit t unclude'sfa. double triode vacuum.: tube [4 .the lefthand sectionjda .of which 'is included with cir-cuit:elementsiL,A C, A5,. l1 and B to .constitute a awell-ikno'wn form of .oscillatorr for .producing i a stablel sinusoidal .wave 116. The .right hand section |411 includes azgrid -I81to whichis connected alresistonnetworkRi, R2 whereby the .sinusoidal wave 1:16- is :translated into a substantially lrectangular; output wave ).20 in the plate circuit .-22. Thematic formappearing onthe grid of tube-14h iszindicat'ed at 24 the. tube operating between a saturation level 2BV and cut-.off-levelvz. The hat portion 26 is .caused Vbygrid current allowing through; the `high 'resistance R1. The rectangular output wave 20 isapplied toiafresistance-capaci- 4U .is shown y.for producing a ,triangularv tance .circuit Ra and C1. 4The action of the high resistances' R3 and R4 in connection with capacitance vCi, which .isalso' fairly large, causes atriangular wave .IZtoappear a'cross'the capacitar-ice C1. Y y I ,lgnforder to apply the vtriangular wave in vpushpull'acrossthefdoublediode rectier tube 30 without adversely aiecting the triangular shape of the'wave prior to rectification, I -providefa couplingtube .3 2 having an input grid 331to which the voltage .Wave 1:2 is applied. Y'Ilhef'tube includes a plateci rcuit .,iland a cathode follower circuit 3 6 which I.iorm twobranch'es 3d, f4 l, d3, ,TZ andlsi, 42, 44, 14.3 ofa parallel circuit to the'lplates .3l and 3 8 :of the .doublediode tubell. Thephase of thewaveg-LZ iisiinvertedfinthe plate circuitll as indicated at |20, but is the saine in cathodeV circuitS asindicatedat 12b. --These two waves are thenvllplldofth 'fgriclsof amplifier tubes fl and 4,2, respectively.A These tubes 'are .each provided with cathode-iollower output connections .43 and 44. respectively, the CIQHQCCiQ 43 y.being connected withfplatef'l and the-connection M being connected gwithplate of the rectier tube 36.

During normal rectiiying operation, the input Wave lf2 will be fully rectified producinga similar triangular wave 4455. vlcurverb, the yfrequency of which is double-theirequency of wave l2. This symmetrical `rectil-ication may be used for time modulation fto A,prodivice symmetricallyv timed pulses. 41.. correa. such .es obtained, by clipping at level l`l5a curveb,jbut preferably the rectification isglvenl a-.predetermined'oi-set biasing condition.

Thisis; accomplished byprovidingthe grid of 'one of-thegampliiier ytubes suchlastubeZ with a given bias -as determined :by the -I'adjustment yof the potentiometer .contact- 46. Thsfin effeci'fy off-sets the zero -axis of the wave i2 for full-wave rectification of.thegwave. For example, the oft-set ams-produced bvthis `prtlefe,lfmrld bios Orl-tube 42Lisindioated bygthebroken line V4 8. The rectic'ationnaccordnggtothefoi-set axisift produces a combinedwave output atte illustratedin solid liness fingcurvegd. It, will be observed'that the portions of the wave l2 above the airis its are smallerthanthe portions below the axis. This produces .Stated @salts 5 Il 452; v53. 545 .55.2156 etc..

which are i-vgroupedV in` lpairs' according .to .the amount rof .o' fset bias. IIhe spacing between .peaksgl an d 52, ,.vforexample; is less than `the spacing .between -the Atrailing .peak of one .pair

and theleading. peak of. the nent Ysucceeding pair,

such as -s-,spacing'f-between .peaks .52 and. 5,3.

provided to clip. the v.peaks along a* .level G2, and

13, The primary coil 1| is coupled to a sourceV of signal energy 14 which may comprise a microphone together with audioamplier stages, A,

etc. The branch circuits 43 and 44 each include one of the secondary coils so that a signal wave applied across the primary 'Il operates to amplitude modulate the triangular wave energy con- The Circuit f Fig 3 is not provided with an @iiset bias, so that the combined wave would resemble wave 45 of curve b. This circuit, however, may be biased similarly as indicated in Fig. 1 if desired. It will also be clear to those skilled in the art that the signal wave amay be introduced in the parallel circuits by substituting multi-grid mixer tubes for tubes 4| and 42 with the signal wave fed to one of the grid circuits of one or both such tubes. ,'The double diode rectifier tube 30 may comprise separate diodes, and, if desired, may com prise dry rectiiier elements or triodes wherein veyed in push-pull manner by circuits 43l and 44. Curve d of Fig. 2 illustrates the push-pull operation of the modulating signal. Assuming that the modulation varies the amplitude of the triangular wave energy with respect to the axis 48 or vice versa, the off-set axis 48 varies with respect to the wave I2, curve a,-the combined output wave 50 of the rectifier tube 3B will shift in time between the wave limit positions 'I6 and T1. Wave position 16, for example, may be regarded as representing the positive polarity limit 16a andwave position 11 as representing the negative polarity limit 11a. It will be understood, of course, that the Vpeaks 5| and 52will be displaced toward or away from each other according to changes in amplitude of the signal wave. Thus, the pulses of curve e vary in time ydisplacement within the limits indicated by the broken lines 18 and 19 depending upon the corresponding instantaneous amplitude of the signal wave.

For time modulation of the symmetrically timed pulses 4'| of curve c, the push-pull modulation occurs between limits symmetrically spaced on oppositesides of the zero axis. As regards the olf-set biasing rectication, it is preferable to have theV lower limit at or above the zero axis, although a negative polarity limit may be desired in some systems.

From the foregoing description itis clear that 'the wave energy I2 in its push-pull application to the rectifier tube 30 Vis not altered `as it would be were it applied through a transformer, that is, from the primary to the secondary coils. The straight line sides of the triangular wave are thus preserved so that the modulating wave may be caused to produce wide swings on the rectifying operation of the wave without introducing distortion as may be the case of a sinusoidal base wave for corresponding wide swings ofmodulation. It will be understood, however, that other shaped waves may be used as the base wave if desired. In fact, a sinusoidal wave may beV applied to the grid 33 of the coupling tube 32 in the same manner, the only precaution required being that the modulating swing be limited to the relatively short portion of the sinusoidal wave adjacent the zero axis thereof, which is approximately linear,

In Fig. 3 I have shown substantially the same circuit arrangement with the exception Vthat the transformer 1|) is provided in the gri-d circuit of the tubes 4| and 42 instead of the cathode circuits 43 and 44. In this embodiment the wave Venergies of the branch circuits 34 and 36 are push-pull modulated according to the signal wave prior to amplification by tubes 4| and 42, -This may be desirable so as to eliminate audio amplifiers in the primary circuit of the transformer 10.

lthe ,input waves-are applied to the grid thereof.

It will also beunderstood that while I have shown a particular form of triangular voltage wave source, Athat 'othercircuit arrangements for producingdesired shaped waves may be substituted therefor.

While I have described above the principles of my invention as applied to certain specific apparatus, it will be evident that niodications of the specific arrangement and structure illustrated and described may be resorted to without departing from thespirit of the inventionl or the scope of the appended claims. Y I f 1. A time modulation system comprising a voltagewave source for furnishing a wave having substantially linearly inclined portions, two rectier means, circuit means for'coupli'ng said wave source in parallel circuit to said two'rectier means, said circuit means'including avac.

uum tube having a grid input circuit and plate and cathode output circuits'forming4 the two legs of said parallel circuit, the plate and cathode circuitsl providing two output waves of opposite phase in response to an input Wave 'on said grid circuit, means combining the outputs of said two rectiermeans whereby a combined wave having spaced peaks is produced', a signal' wave/"source, and means to amplitude modulateV said two` output waves in push-pull operation according to said signal wave, whereby .the timing of said peaks is modulated according to variations in said signal Wave. f

2. The system dened in claim 1 wherein the circuit means includes two Vparallel branches each having an amplifier, and means to provide at least oneV of said amplifiers with a given offset bias. Y

3. The system defined in claim 1 wherein the means for amplitude modulating the two output Waves includes a transformer having a primary coil and two secondary coils, means connecting the primary .coil to said signal wavev source, means connecting one of said'secondary coils in one branch of the parallel `circuit and means for connecting the other of'said secondary, coilsl in the other branch Yof saidV parallelV circuit.

4. The system deiined'in claim 1 wherein the circuit means` 'includes two parallel Lbranches each. having Van amplier, and-the means-,for amplitude modulating the two output `waves in pushpull operationV is coupled to V.said circuit means ahead of said arnpliers;

' f5. The systemV defined in` claim 1 wherein the circuit 'means Vincludes .two parallelbranches each having'an amplier, and the means for amplitude modulating the Vtwo output waves in push-pull operation -is Coupled to said circuit Ameans following said amplifiers. i

vportions' if-said combined wave.l

l'1. The system defined in claim 1 wherein the voltage wave source includes a stable oscillator, means for translating the sinusoidal wave output of said oscillator into a substantially rectangular wave, and means to translate said restan-- gular wave into a triangular wave, having substantially theV same slope for the leading and trailing edges of each undulation thereof.

8. A time modulation system comprising a voltage wave source for furnishing a wave having substantially linearly inclined portions, iirst and second wave transmission means, each of said transmission means having a threshold clipping level for passing energy according to those portions of the wave applied thereto which extends beyond the threshold clipping level thereof, circuit means for coupling said wave source in parallel circuit relation to said first and said second transmission means, said circuit means including a tube having a grid input circuit and plate and cathode output circuits, the plate and cathode circuits providing two output waves of opposite phase in response to an input wave on said grid circuit, each of said rst and said second transmission means responding to those wave portions of said output waves which extend in proper polarity direction beyond the threshold level thereof, means for combining the outputs of said rst and said second transmission means whereby a combined wave having sharp peaks is produced, a signal Wave source, ,and means to vary the amplitude of said two output Waves in push-pull operation with respect to said threshold levels according to amplitude variations in said signal wave.

9. In combination, means for generating ra sawtooth signal, means for deriving paired phase displaced sawtooth signals from said sawtooth signal, a source of modulating signal, and means responsive to said source of modulating signal comprising rectier means having a single ended output circuit for time modulating and combining the peaks of said phase displaced sawtooth signals.

10. In combination, a source of sawtooth Waves, means for deriving from said sawtooth waves pairs of phase displaced sawtooth waves, means for diierentially modulating said pairs of phase displaced sawtooth waves comprising a push-pull rectier means having a single ended output circuit for combining said modulated waves.

11. In combination, a source of modulating signals, a source of phase opposed sawtooth signals, means responsive to said modulating signals for relatively time modulating said sawtooth signals and comprising a pair of rectifiers, means for applying successively timed sawtooth' signal components to alternate ones of said pair of rectiers, means for biasing said rectiiiers in response to said modulating signals and means for combining said modulated sawtooth signals.

12. A combination in accordance with claim 11 wherein said modulating means are statically biased differentially.

13. The combination comprising two rectier means, circuit means for coupling a voltage wave source in parallel circuit to said two rectifier means, said circuit means including a vacuum tube having a grid input circuit and plate and cathode output circuits, forming the two legs of said parallel circuit, the plate and cathode output circuits providing two output waves in opposite phase in response to an input Wave on said grid circuit, means for combining the outputs of said two rectiers means whereby a fully rectified wave is produced, means to modulate the operation of the rectier means comprising a transformer having la primary coil and two secondary coils, a source of modulating voltage connected to said primary coil, one branch of the parallel circuit of lsaid circuit means including one of said secondary coils and the other branch thereof including the other of said secondary coils.

NORMAN H. YOUNG, JR.

REFERENCES CITED The following references are of record in the 40 file of this patent:

UNITED STATES PATENTS 

